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Abstract:

A method for retrofitting an existing steam turbine with a steam
extraction facility is provided. The stem turbine has a plurality of
pressure stages and is integrated into a fossil-fired steam power plant.
A steam extraction line is connected to one pressure stage or between two
pressure stages of the steam turbine, and a heating steam turbine is
connected into the steam extraction line.

Claims:

1-5. (canceled)

6. A method for retrofitting a steam turbine with a steam extraction
capability, the steam turbine comprising a plurality of pressure stages
and being integrated into a fossil-fired steam power plant, comprising:
connecting a steam extraction line to one pressure stage or between two
pressure stages of the steam turbine; and connecting a heating steam
turbine into the steam extraction line.

7. The method as claimed in claim 6, wherein the steam extraction line is
connected to a hot reheat line of the steam turbine.

8. The method as claimed in claim 6, wherein the steam extraction line is
connected to a cold reheat line of the steam turbine.

9. The method as claimed in claim 6, wherein the steam extraction line is
connected to an overflow line of the steam turbine.

10. A fossil-fired power plant, comprising: a steam turbine comprising a
plurality of pressure stages and being integrated into the fossil-fired
steam power plant, wherein the steam turbine is adapted to perform a
method for retrofitting the steam turbine with a steam extraction
capability as claimed in claim 6.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is the US National Stage of International
Application No. PCT/EP2011/071180 filed Nov. 28, 2011 and claims benefit
thereof, the entire content of which is hereby incorporated herein by
reference. The International Application claims priority to the German
application No. 10 2010 062 623.6 DE filed Dec. 8, 2010, the entire
contents of which is hereby incorporated herein by reference.

BACKGROUND OF INVENTION

[0002] There is a need to adapt existing fossil-fired power plants to
changing requirements. Steam power stations or combined-cycle gas and
steam power stations in particular are often subject to demands for
adaptation, especially for a retroactive implementation of the capability
to extract steam from the steam section of the power station. This
additionally extracted steam can be required as process or heating steam
for internal processes within the power station process or for supplying
other processes outside of the actual power station process. Extracting
steam from the steam turbine process reduces the remaining steam volume
which is still available for the steam turbine process and which now can
make no further contribution to the generation of steam. As a consequence
the extraction of steam from the steam turbine process reduces the
efficiency of a steam power plant.

[0003] In order to enable a thermodynamically optimized concept to be
realized in a steam extraction retrofit that is now to be implemented,
the use of an extraction turbine would recommend itself already at the
time of construction of the power plant. However, this concept would lead
to an increased initial investment since the turbine cannot be optimized
simultaneously for operation without extraction and with extraction.
Retrofitting a steam turbine plant with steam extraction capability is
often technically demanding and complex, as well as cost-intensive in
terms of implementation. If a steam extraction capability is realized
only as a result of a retrofit, substantial losses in efficiency are
likely into the bargain.

[0004] Converting an existing steam turbine plant to provide a retroactive
steam extraction capability, in particular for tapping low-pressure
steam, can be very complicated and labor-intensive, however. Thus, for
example, the dimensions of the power house may not be sufficiently large
to accommodate the additional piping for extracting the steam, or the
steam turbine or, as the case may be, the power station process is not
suitably configured for steam extraction. In steam turbines having a
separate casing for the medium- and low-pressure stages it is at least
easily possible to tap low-pressure steam at the overflow line. In steam
turbines having a medium- and low-pressure stage housed in a single
casing, on the other hand, it is often not feasible to carry out
retrofits in order to extract the large volume of steam required, for
which reason the turbine has to be replaced in this situation. In any
event, however, when low-pressure steam is tapped into the low-pressure
section from the overflow line, the low-pressure section needs to be
adapted to handle the changed swallowing capacity (steam volume flow).

[0005] Extracting steam from other sources within the power station
process is often likewise not cost-effective or possible in a suitable
manner. Thus, for example, extracting steam from a reheat line of the
steam turbine leads to load imbalance in the boiler if no further
expensive and complex measures are taken. Extracting higher-value steam
for the carbon dioxide separator must also be ruled out unless further
measures are undertaken, since this leads to unacceptable energy losses.

[0006] A further problem that arises with the retrofitting of a steam
extraction capability is that when the steam extraction is discontinued
the steam that is now not required abruptly accumulates to excess. This
surplus steam now cannot simply be returned to the steam turbine process,
because the latter is configured for operation with steam extraction, in
other words for a lower volume of steam.

SUMMARY OF INVENTION

[0007] The object of the invention is therefore to disclose a method for
retrofitting a steam extraction capability in order to tap steam from the
steam process of a fossil-fired power plant, which capability can be
realized in a simple and cost-effective manner, and which in addition is
thermodynamically favorable, so that the efficiency losses due to the
additional steam extraction are minimized.

[0008] The object is achieved according to the invention by the features
of the independent claims. Also provided according to the invention is a
heating steam turbine which is connected to the overflow line of the
steam turbine.

[0009] The invention permits an extraction point to be chosen which lies
outside of the turbine. This enables retrofit capability to be integrated
without high initial investments. The use of a back-pressure turbine with
extraction points permits multistage heating to be realized, which is
more beneficial thermodynamically than single-stage heating. Moreover,
this retrofit concept permits retroactive thermodynamic optimization,
since the extractions are only specified at the time of the retrofitting.

[0010] According to the invention the heating steam extraction is
decoupled from the main process through the use of the back-pressure
steam turbine. Because the back-pressure steam turbine is not supplied
until the time of conversion, no extraction points need to be provided on
the main steam turbine. This means that retrofitting is possible even in
a power station in which heating steam extraction was not included in the
planning at the time of installation. In this case, however, it might be
necessary to carry out a modification to the low-pressure turbine.

[0011] Advantageously the steam extraction line is connected to a reheat
line. In the event of a deactivation of the steam extraction function the
low-pressure steam continues to be tapped from the overflow line. For
this reason an auxiliary condenser is connected in parallel with the
steam extraction line. The auxiliary condenser is provided so that in the
event of failure or intentional deactivation of the steam extraction
function the accumulating excess steam will be condensed in the auxiliary
condenser.

BRIEF DESCRIPTION OF DRAWINGS

[0012] Exemplary embodiments of the invention are explained in more detail
below with reference to figures, in which:

[0013]FIG. 1 is a schematic diagram of a steam turbine arrangement
comprising a back-pressure steam turbine according to the invention,

[0014]FIG. 2 is a schematic diagram of a steam turbine arrangement having
steam extraction from the overflow line according to the prior art.

DETAILED DESCRIPTION OF INVENTION

[0015]FIG. 2 shows a steam turbine arrangement having steam extraction
from the overflow line according to the prior art. The steam extraction
serves in this case to provide a district heating supply using two
heating condensers HZ-K. The district heating system is connected to the
gas and steam turbine power plant via the overflow line of the steam
turbine. There, steam (NAA) is extracted and ducted by way of a steam
line from the power house UMC to the district heating building UND. The
actual district heating system in the form of 2×50% heating
condensers is located in the district heating building UND. Depending on
the required district heating capacity, provision of the district heating
is effected using a single stage. The two district heating preheaters in
combination can thermally transfer 265 MW at the maximum into the
district heating system during normal operation.

[0016] Alternatively the district heating system can also be operated with
steam from the cold reheat cycle (KZU) (emergency operation during steam
turbine downtime). Capacity transfer into the district heating grid is
thermally limited in this case.

[0017] The district heating return-circuit water that is to be heated is
provided at the transfer point at a pressure of approx. 5-22 bar and
flows via the two steam-heated district heating preheaters (HzVW1 and
HzVW2) back into the district heating flow line to the district heating
loads. The district heating flow line and the district heating return
line can each be separated from the district heating water grid by means
of a motorized butterfly valve. Each HzVW can be shut off individually by
means of a manually operated shutoff valve on the input side and by means
of a motorized butterfly valve on the output side. They possess a common
bypass fitted with a motorized valve.

[0018] The steam for the two HzVWs is tapped during steam turbine
operation from the overflow line to the low-pressure (ND) steam turbine
(DT) by way of a motorized bleeder valve. Two nonreturn valves in the
line prevent backflow to the DT. A steam inspection probe monitors
compliance with the maximum permitted pressure in this line. If the set
value is exceeded the medium-pressure (MD)DT quick-action shutoff valve
is closed. The DT steam extraction lines are drained via drainage lines
fitted with motor-driven shutoff valves to the condenser MAG and
preheated. In order to achieve an energetically favorable mode of
operation the HzVWs are connected to the system in a staggered manner:
For that purpose the bypass of the HzVWs is set to fully open before the
district heating steam extraction process is placed into service. The
control butterfly valves at the outlet of the HzVWs are closed and the
heat extraction begins with the opening of the outlet valve of the HzVW1.
After the open position is reached the control butterfly valve in the
bypass closes in a controlled manner in order to increase the district
heating capacity. As the demand for heat increases the control butterfly
valve at the outlet of the HzVW2 is opened in a controlled manner and, as
previously in the case of HzVW1, closes the control butterfly valve in
the HzVW as the demand for heat increases further until the entire volume
flows through the HzVWs. If both HzVWs are in operation with the bypass
closed and the requirement for heating capacity continues to increase,
the steam pressure in both HzVWs is raised with the aid of the control
butterfly valve in the overflow line to the ND turbine and as a result
the heat output is increased in a controlled manner. In bypass operation
of the steam turbine the steam is tapped from the KZU by way of a steam
converter station. A steam inspection probe monitors to ensure compliance
with the maximum permitted pressure on the low-pressure side. If the set
value is exceeded the corresponding converter valve is immediately
closed. Any valve leakages that could lead to a further increase in
pressure are in each case ducted to the atmosphere via a downstream
safety valve. The injection water for cooling the steam of the steam
converter station is taken from the condensate system downstream of the
condensate pumps. In order to protect against contamination of the
injection control fittings the injection water lines are fitted with an
upstream dirt strainer. In addition the section of pipeline up to the
control valve may be protected by means of a safety valve in certain
cases in order to ensure it cannot be damaged due to heating of the
enclosed condensate. The steam lines upstream of the steam converter
stations are preheated and drained to the drainage system LCM via
drainage lines fitted with motor-driven shutoff valves. As the
requirement for district heating capacity decreases the HzVWs are powered
down in precisely the reverse order to the connection sequence.

[0019] The condensate in the HzVWs drains off geodetically or due to the
pressure difference into the main condenser, being ducted in the process
through a main condensate preheater in order thereby to operate more
energy-efficiently. A control valve in the drain line keeps the fill
level in the HzVWs constant within the predefined limits. The two HzVWs
remain under pressure on the hot water side when the district heating
system is not in operation so that an escape of steam is reliably
prevented. Both HzVWs are fitted with a safety valve on the hot water
side in order to discharge the expanding heating water in the event of
heating and enclosed medium. Valves and fittings that are operated in the
vacuum range have a water seal adapter or are implemented with
vacuum-tight stems. The impulse lines of the fill level measurements of
the HzVWs are kept filled at all times by way of bubbler lines. A safety
valve is installed on both HzVWs in order to enable the accumulating
heating water to be ducted away in the event of pipeline rupture or
leaks.

[0020] The district heating system according to FIG. 2 has the following
tasks:

[0021] ensuring heat input into the district heating grid

[0022]
regulating the flow line temperature

[0023] the mass flow rate is
regulated on the power station side

[0024] Example process parameters:

[0025] return line temperature:
60-75° C.

[0026] flow line temperature: 90-110° C.

[0027]
heating water mass flow rate: max. 1400 kg/s

[0028] district heating
capacity: approx. 20-265 MW.

[0029] The district heating system consists of the following main
components:

[0034]FIG. 1 shows a steam turbine arrangement comprising a back-pressure
steam turbine according to the invention.

[0035] The district heating system is connected to the gas and steam
turbine plant exactly as in FIG. 2. Steam (NM) is extracted from the
overflow line of the steam turbine (DT) and ducted by way of a steam line
from the power house UMC to the district heating building UND. Located
there is a heating steam turbine including all ancillary equipment
necessary for operation, such as e.g. lubricating oil system, evacuation
system and drainage facilities. The steam from the NM system is ducted
either to the steam turbine only or additionally to a third heating
condenser (HzVW3). The heating power output of the district heating
system is realized in up to three stages depending on the district
heating capacity required. Accordingly, two or even three heating
condensers are operated on the steam side as a function of demand. A
heating condenser (HzVW1 and HzVW2) is located under each steam turbine
outflow. Operating in combination at maximum steam turbine load, these
heating condensers can transfer, for example, 120 MW equivalent thermal
energy from the NM steam system into the district heating grid. If an
increased steam output of more than 120 MW equivalent thermal energy is
to be extracted, steam is injected into the heating condenser 3 (HzVW3)
in addition. The latter is supplied directly with steam from the NM
system. Alternatively the district heating system can also be operated
with steam from the cold reheat cycle (KA) (emergency operation during
steam turbine downtime). Capacity transfer into the district heating grid
is thermally limited to, for example, 220 MW in this case. In the event
of downtime/failure of the heating steam turbine the entire district
heating output can be transferred into the district heating grid by way
of the HzVW3. In this case the steam supply to the heating steam turbine
is interlocked and the steam is supplied exclusively to the HzVW3.

[0036] The district heating system according to FIG. 1 has the following
tasks:

[0037] ensuring heat input into the district heating grid

[0038]
regulating the flow line temperature

[0039] the mass flow rate is
regulated on the power station side

[0040] Example process parameters:

[0041] return line temperature:
60-75° C.

[0042] flow line temperature: 90-110° C.

[0043]
heating water mass flow rate: max. 1400 kg/s

[0044] district heating
capacity: approx. 20-265 MW.

[0045] The district heating system consists of the following main
components:

[0049] The district heating system can be housed in a separate building
UND. A larger district heating building may be necessary on account of
the increased space requirement for the heating steam turbine incl.
ancillary equipment.

Patent applications by Andreas Pickard, Adelsdorf DE

Patent applications in class Including production of withdrawable product or steam for external use

Patent applications in all subclasses Including production of withdrawable product or steam for external use